This is probably such a rediculous question to ask, bet here goes;

What wold happen if I coupled my Freesat TV with my Foxsat HDR via the LNB out port?

You get a limited functionality, the LNB out is really for use with a completely different kind of LNB.

hdr off - full channel choice on the TV.

hdr-on - only channels in the same frequency band (high/low) and polarity (horizontal/vertical) as the transponder tuner 1 is currently using.

Best by far to run a 3rd cable from your lnb which is most likey a quad

I use LNB out to create a loopback adapter, as I only have single LNB dish. I can live with the limitation that I can only view channels on the same polarization if one is being recorded. I have 4 tuners on my Windows Media Center, so it is not a big problem.